Nowadays, laminated cores have been adopted in the power transformers with a voltage class of 110 kV or above. A laminated core is formed from shaped silicon steel sheets which are processed in slitting and shearing production lines and laminated. The major disadvantages of the laminated core include: firstly, there are many air gaps formed by the seams in the magnetic circuits, causing greater magnetic resistance and consequently larger no-load loss and no-load current; secondly, the direction of the local magnetic circuits is not in conformity with the high magnetic direction of the silicon steel sheets; thirdly, the sheets are not close enough, this not only reduces the lamination factor, but also increases the noise; fourthly, the three phase currents are not balanced due to unbalanced three-phase magnetic circuits. To sum up, the laminated core power transformers have some obvious defects, and therefore there is a need for those skilled in the art to improve these power transformers.